1. Pediatric Patellar Instability : Imaging
John A. Schlechter, DO, FAOAO
Richard Michelin, DO
Children’s Hospital Orange County, Orange, CA

2. Pediatric Patellar Instability : Imaging
Radiographs
Standing alignment film CT
MRI
Bone Age
Assessment of Risk Factors

3. Pediatric Patellar Instability : Imaging
Radiographs

4. Radiographs Standing Anteroposterior True lateral
Notch (tunnel / Ferguson view)
Merchant

5. What is a true lateral radiograph?
30º knee flexion
Femoral condyle overlap with superimposition of the condyles
Open patellofemoral joint space 
Slight superimposition of the fibular head and tibia 
NOT ALWAYS EASY TO REPEATEDLY
GET ” PERFECT”
LATERAL KNEE X-RAYS

6. The role of a true lateral radiograph in PF instability
Assess
patella height
Trochlea depth
Trochlea morphology
Jaquith BP Parekh SN, J Pediatr Orthop 2017 Oct/Nov; 37(7)

7. Trochlea Depth as measured on a lateral x-ray
Dejour H, Walch G, Nove-Josserand L, Guier Ch. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 1994

8. Standing alignment radiograph
Full length – hips to ankles
Assessment of coronal plane deformity
Valgus alignment predisposes to PF Instability
Malalignment test
Mechanical axis deviation
mechanical Lateral Distal Femoral Angle (mLDFA)
Medial Proximal Tibial Angle (MPTA)

9. Radiographic Assessment of LE Deformity
AP view Lower Extremity
36” or 51” long films

10. Mechanical Axis of LE
MAD (mechanical axis deviation) = 10 mm medial

11. Stevens P Strategies in Trauma and Limb Recon. 1 (1) Dec 2006

12. Frontal Plane
mLDFA = 88°
MPTA = 87°

13. Pediatric Patellar Instability : Imaging
Computed Tomography (CT)

14. CT
Assess for osteochondral defects / fracture / bony component of fracture size
Osseous morphology of the trochlea
Assess risk factors for PF Instability
“Gun site” view for rotational profile
Tibial tubercle - trochlea groove (TT-TG) distance
Has a role but due to radiation exposure in children has been replaced in most instances by Magnetic Resonance Imaging

15. Pediatric Patellar Instability : Imaging
Magnetic Resonance Imaging (MRI)

16. MRI - fundamental assessments and measurements
Medial patellofemoral ligament injury
Cartilage integrity – especially medial facet patella and lateral femoral condyle
Very useful to assess risk factors for PF instability
Combined MPFL Injury
Seeley M, Bowman KF, Walsh C, Sabb BJ, Vanderhave KL. Magnetic resonance imaging of acute patellar dislocation in children: patterns of injury and risk factors for recurrence. J Pediatr Orthop 2012

17. MRI in Patellofemoral Instability
Osteochondral fracture
MRI assess all cuts - can settle anywhere
Look posterior
Often adhered to the medial or lateral femoral condyle
Seeley MA, Knesek M, Vanderhave KL. Osteochondral injury after acute patellar dislocation in children and adolescents. J Pediatr Orthop 2013

18. Pediatric Patellar Instability : Imaging
Bone Age Assessment

19. Bone Age ? when chronologic age ≠ physiologic age
Assessment of skeletal maturity
Guides treatment and pre operative planning of physeal sparing procedures
Nelitz M, Arch Orthop Trauma Surg (2012) 132:1647–1651

20. Bone Age Assessment
Radiographic Atlas of the Hand and Wrist (Greulich & Pyle Method)
Shorthand Bone Age Assessment
The Sauvegrain Method
Modified Sauvegrain Method
Tanner-Whitehouse III Method
Smartphone Applications

21. Greulich and Pyle Method
Developed in 1959, the Radiographic Atlas of the Hand and Wrist has historically been considered the gold standard
Disadvantages of this method are
Subjective analysis of morphologic changes with long intervals between reference standards during the critical pubertal growth period
Requires access to hard copy of atlas
Requires sufficient training to perform the technique
Depends on patient having normal left-hand radiograph

22. Shorthand Bone Age Assessment
Abbreviated method of bone age assessment based on Greulich and Pyle principles
Much simpler method that can be easily referenced or committed to memory
High intraobserver and interobserver reliability
Similar disadvantage in that it requires a normal left-hand radiograph
Heyworth BE, Osei DA, Fabricant PD, et al. The shorthand bone age assessment: a simpler alternative to current methods. J Pediatr Orthop 2013

23. Shorthand Bone Age M/F Finding M F Appearance of hook of the hamate
12.5 10
Thumb Sesamoid Appearance 13 11
Capping Distal Radius 14 12
Closure Thumb DP 15
Closure Index DP
15.5
13.5
Closure Index PP 16
Closure Index MC
Capping radius = rounded osseous peak oriented proximally on the ulnar side
Closure = >50% closed
Heyworth BE, Osei DA, Fabricant PD, et al. The shorthand bone age assessment: a simpler alternative to current methods. J Pediatr Orthop 2013

24. Shorthand Bone Age Assessment
Heyworth BE, Osei DA, Fabricant PD, et al. The shorthand bone age assessment: a simpler alternative to current methods. J Pediatr Orthop 2013

25. The Sauvegrain Method
Determines skeletal age using AP/Lateral radiographs of left elbow
27 point scoring system based on four anatomic structures:
The lateral condyle
The trochlea
The olecranon apophysis
The proximal radial epiphysis
The score is plotted on a graph to calculate skeletal age
Score of ≥ 26 indicates child has passed peak height velocity
Addresses limitations of the shortand and Greulich-Pyle methods
Dimeglio A, Charles YP, Daures JP, De Rosa V, Kabore B. Accuracy of the sauvegrain method in determining skeletal age during puberty. J Bone Joint Surg 2005

26. The Modified Sauvegrain Method
Simplified method condensing the evaluation of four different ossification centers of the elbow to one
Shown to be reliable and accurate
Olecranon maturation correlates with pubertal growth spurt and Risser grade 0, helping identify patients who are skeletally immature
Closure of the olecranon epiphyses indicates end of accelerated growth spurt and entering of deceleration phase
Dimeglio A, Charles YP, Daures JP, De Rosa V, Kabore B. Accuracy of the sauvegrain method in determining skeletal age during puberty. J Bone Joint Surg 2005

27. Tanner-Whitehouse III Method
Previously, skeletal maturity assessment of radius, ulna, and small bones of hand
Found to be most associated with timing of scoliosis curve acceleration phase (Sanders et al, 2007)
Cumbersome method that requires use of an atlas
Simplified version created for clinical purposes, using only small bones of hand found to be reliable and accurate (Sanders et al 2008)
Sanders JO, Khoury JG, Kishan S, Browne RH, Mooney JF, Arnold KD, McConnell SJ, Bauman JA, Finegold DN. Predicting scoliosis progression from skeletal maturity: a simplified classification during adolescence. J Bone Joint Surg 2008

28. Smartphone Applications
Allow for quicker and more convenient assessments of:
Bone age
Limb-length inequality and Limb Deformity Assessment
Timing of epiphysiodesis

29. Pediatric Patellar Instability : Imaging
Assessment of Risk Factors

30. Assessment of Risk Factors
Trochlea dysplasia
True lateral x-ray, MRI
Genu Valgum
Standing alignment film
Pan genu torsion
CT or MRI rotational profile
MPFL disruption
MRI trans-axial cuts
Patella alta
Lateral radiographs and Sagittal MRI – Caton Deschamps Ratio and Patella tendon length

31. Assessment of Risk Factors – Patella Alta
The Caton-Deschamps index (CDI) is defined by the
ratio between the articular facet length of the patella
(AP) and the distance between the articular facet of the
patella and the anterior corner of the superior tibial
epiphysis (AT). CDI = AT/AP
NORMAL = 1 range
> 1.3 predisposes to instability
J Bone Joint Surg Am. 2011;93:e35(1-5)

32. Assessment of Risk Factors – Patella Alta
The Caton-Deschamps index is a simple and reliable index measure on Lateral radiographs of the knee for evaluating patellar height in children as well as adults.
It is an alternative to the Insall-Salvati index measurement, in which reproducibility is poor due to difficulties in determining the distal point of the patellar tendon, and to the Koshino index, which is complex to use.
J Bone Joint Surg Am. 2011;93:e35(1-5)

33. Assessment of Risk Factors – Trochlea Dysplasia
Dejour Classification – True Lateral radiograph
LOW GRADE
Type A - crossing sign (the deepest part of the trochlea crosses the most anterior part of the lateral femoral condyle)
Dejour H, Walch G, Nove-Josserand L, Guier Ch. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 1994

34. LOW GRADE - Dejour type A
Dysplasia type A - line of the trochlear groove is seen to intersect the anterior border of one of the condyles (“crossing sign”) on CT images the trochlea appears practically normal
Berruto M, Ferrua P, Carimati G, Uboldi F, Gala L. Patellofemoral instability: classification and imaging. Joints 2013

35. Assessment of Risk Factors – Trochlea Dysplasia
Dejour Classification – True Lateral radiograph
HIGH GRADE
Type B - supratrochlear spur or bump (bulge of the proximal trochlea)
Type C - crossing sign + double contour sign that goes distal to the crossing sign (hypoplastic medial condyle),
Type D shows all of the signs on lateral x-ray
Dejour H, Walch G, Nove-Josserand L, Guier Ch. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 1994

36. Dejour D, Le Coultre B; Sports Med Arthrosc Rev 2007;15:39–46

37. Crossing Sign
Supratrochlear Spur/Bump
Double Contour
Vertical Joint or Cliff Pattern
Lippacher et al. AJSM Vol 40. No

38. Dejour D, Le Coultre B; Sports Med Arthrosc Rev 2007;15:39–46

39. Assessment of Risk Factors – Trochlea Dysplasia
True lateral radiograph
Dejour classification signs of trochlear dysplasia
crossing sign Dejour A
trochlear bump Dejour B
double contour Dejour C
Jaquith BP Parekh SN, J Pediatr Orthop 2017 Oct/Nov; 37(7)

40. Assessment of Risk Factors – Trochlea Dysplasia
Lateral trochlear inclination (LTI)
Fat suppressed T2-weighted MRI images
Measured on first craniocaudal axial image that demonstrates cartilaginous trochlea
Angle formed between the tangential line to the posterior aspect of femoral condyles and the tangential line to the subchondral bone of the lateral trochlear facet
Carrillon Y, Abidi H, Dejour D, Fantino O, Moyen B, Tran-Minh VA. Patellar instability: assessment on MR imaging by measuring the lateral trochlear inclination – initial experience. Radiology 2000

41. Assessment of Risk Factors – Trochlea Dysplasia
Patellar instability mean value = 6.17°
Control group mean value = 16.93°
Trochlear dysplasia LTI threshold= < 11°
Carrillon et al, Radiology 2000; 216:582–585

42. Assessment of Risk Factors – Lateralization of the Tibial Tubercle
Tibial tubercle - trochlea groove (TT-TG) distance
Best done on Axial CT
Can be done on MRI
Dejour H, Walch G, Nove-Josserand L, Guier Ch. Factors of patellar instability: an anatomic radiographic study. Knee Surg Sports Traumatol Arthrosc 1994

43. CT: TT-TG Distance
Medial/Lateral distance between the tibial tubercle and trochlear groove
Average = 10 – 12 mm
Abnormal = > 20 mm
CT is more accurate method when compared to MRI as MRI may underestimate distance (Camp et al) (Ho et al, 2015)
Beaconsfield T, Pintore E, Maffulli N, Petri GJ. Radiological measurements in patellofemoral disorders. Clin Orthop Relat Res 1994
Camp CL, Stuart MJ, Krych AJ, Levy BA, Bond JR, Collins MS, Dahm DL. CT and MRI measurements of tibial tubercle-trochlear groove distances are not equivalent in patients with patellar instability. Am J Sports Med 2013

44. The TT-TG distance can be measured with excellent interrater reliability on both MRI and CT; however, the values derived from these 2 tests may not be interchangeable. This observation should be taken into consideration when MRI is used for surgical planning because MRI may underestimate the TT-TG distance when compared with CT.
American Journal of Sports Medicine, Vol. 41, No

45. Assessment of Risk Factors – Pan Genu Torsion
Pan genu torsion also know as Miserable malalignment
Increased femoral anteversion
External tibial torsion
Axial CT
Can be done on MRI
Liodakis et al. Skeletal Radiol (2012) 41:305–311
Muhamad et al. J Child Orthop (2012) 6:391–396